Such tools may comprise a base plate of generally annular form from which pillars extend. On the pillars is mounted a structure movable towards and away from the base plate. The structure includes a driving motor, usually an electric motor, on whose output shaft is mounted a collet for receiving a tool bit of a configuration appropriate to the task to be performed. On moving the structure towards the base plate, the tool bit moves through the central aperture in the base plate and into engagement with the work piece.
The tool is fitted with a depth gauge that is set by a user and determines the extent of the downward movement of the structure. The extent of the downward movement of the structure determines the extent of movement of the bit and it is clearly important that the user be able to set the gauge accurately, easily and quickly.